Journal of the Japan Society of Erosion Control Engineering, Vol.62,No.2,2009

Slope failures in and around a large]scale abandoned forest after clear]cutting, southern Kyushu, Japan

Yasuo MIYABUCHI and Hitoshi TANAKA


Abstract

Abandonment of forest plantations after clear]cutting has increased in the southern part of Kyushu, SW Japan. This abandonment of forests after clear]cutting hinders sustainable forest management and recovery of forest resources, and poses a periodic threat to soil and water resources. We investigated the current status of slope failures in and around a large]scale abandoned forest (95.6ha) after clear]cutting, located near Kumamura Village, southern Kumamoto Prefecture. Dominant geology in the investigated area is alternating beds of sandstone and mudstone, dipping to the northwest, within the Shimanto Belt (an accretionary prism). Geologic characteristics affect the distribution of slope failures in this region. We divided the slope failures into three types: shallow road]cut failures on NW]N facing dip slopes along harvesting roads, slumps in road prism and fill, and deep]seated landslides on SE]S facing opposite dip slopes along the Butsuzo tectonic line (the boundary between the Chichibu and Shimanto terrains). Although slope failures along harvesting roads are affected by geologic characteristics, they are primarily related to inadequate road construction. In contrast, deep]seated landslides along the Butsuzo tectonic line are predominantly influenced by geologic structure in this region, independent of logging and road construction. This study provides a rough guide for planning the design and construction standards of forestry related roads and associated drainage systems to minimize landslide hazards.

Key wordsFabandoned forest, clear]cutting, slope failure, geologic characteristics, southern Kyushu


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